Each year in the United States approximately 13 million units of blood are used for transfusion or to generate life-saving blood products such as platelets. Voluntary blood donation is utilized by the Red Cross and other agencies to procure from about 500 mL to about 1000 mL whole blood samples. Self-screening of voluntary donation is relatively safe and effective in the US and Western Europe where the incidences of HIV and other adventitious pathogens are relatively low. However, in countries in which HIV and hepatitis are endemic, procurement of safe blood for transfusion can be highly problematic. As an alternative to voluntary blood donation many groups have attempted to develop safe artificial blood substitutes that could undergo long-term storage. While some of these products show significant promise in transiently treating traumatic blood loss, such products are not designed for long-term substitution of red blood cell function. Increasingly there is a need to develop a safe and plentiful supply of erythrocytes that can be administered to patients on the battlefield or civilian hospital settings around the world.
Conventional methods for producing erythrocytes are either inefficient, too small in scale, or too laborious to allow for the continuous, on-site production of erythrocytes. Conventional dish or flask-based culture systems are associated with discontinuous medium exchange, and generally dish-based culture systems cannot be used to handle single batches of >109 cells. A logical further development from dishes are bag technologies, e.g. the Wave Bioreactor, in which the medium volume is significantly enlarged by using bags and cell attachment surface can be enlarged by using buoyant carriers. However, bag-type reactors typically operate from 2×106 to about 6×106 cells/ml medium, requiring significant media dilution during culture and a laborious 10-100 fold debulking. Moreover, bag technologies, and generally all large-vessel stirred tank type bioreactors, do not provide tissue-like physiologic environments that are conducive to “normal” cell expansion and differentiation.